1. Field of the Invention
This invention relates to locks having key-controlled removable and installable cores and, more particularly, to such locks in which the core must be rotated to a specific position before the removal or installation can be effected.
2. Description of the Prior Art
The use of cylinder locks in connection with various pieces of equipment, such as cabinet drawers and the like, is well known. Various forms of such locks have been constructed for diverse applications, the specific configuration of any particular lock being a function of the particular application. In one such configuration, typically used for locking cabinet drawers and the like, the lock controls a latch member or cam which is engageable with a keeper for locking the drawer. Typically, the latch member or cam is engaged with a shifter which is rotatable within the rear end of the cylindrical housing of the lock and is, in turn, engageable with a key-operated core rotatably disposed in the forward end of the housing. Absent the key, combinating tumblers in the core, which may be disks or pins, are biased into longitudinal grooves or splines in the housing to prevent rotation. When the combinating tumblers read a properly bitted key inserted in a keyway in the core, they are retracted within the core to accommodate rotation of the core between locked and unlocked positions. Each groove may be paired with a companion, diametrically opposed groove, to allow the tumblers to shift about as the key is inserted and withdrawn.
It is often necessary to replace the core. To this end, various constructions of removable lock cores have been developed, wherein the core is usually removable by means of a special release or control key which is intended to operate a special retaining tumbler once the lock core is manipulated into a certain release position by the standard key. Exemplary locks of this type are disclosed, for example, in U.S. Pat. Nos. 5,101,649 and 5,119,654, in each of which locks the core is removable only when disposed in its unlocked position. When such a lock is used in an application utilizing a rotatable latch cam and shifter, the core decouples from the shifter as a result of removal from the housing. While the core can be removed and reinstalled in only a single rotational position relative to the housing, once it is removed the shifter might accidentally be rotated so that, upon reinstallation of a new core, the shifter is no longer in a proper rotational orientation relative to the core. Thus, when the core is rotated to its locked position, the latch cam may not actually be in engagement with the keeper.